SPRAY DEPOSITION AND DRIFT FROM TWO “MEDIUM” NOZZLES

Abstract

The labels of many crop protection and production materials include specific directions for application, such asapply as a MEDIUM spray. Therefore, aerial applicators are utilizing computer models and printed materials to complywith these labels. The objective of this study was to determine spray deposition and drift from two medium nozzles usedin an aerial application. With an application rate of 28 L/ha (3 gal/acre), CP nozzles were configured to produce a volumemedian diameter (DV0.5) of 304 .m (T1) and Spraying Systems D8 straight stream nozzles were configured to produce a DV0.5of 413 .m (T2). Under the ASAE nozzle classification system, both would be classified as medium sprays; however, the sprayvolume contained in droplets less than 200 .m was 15.0% and 8.7% for the CP and D8 nozzles, respectively. These studiesshow that very different downwind deposition can occur from two aerial spray nozzles that are classified as medium basedon droplet spectra. One nozzle setup (T1) contained two times more spray volume in droplets less than 200 .m compared tothe second nozzle setup (T2). As a result of this difference, T1 produced significantly higher downwind drift deposition thanT2. At 50 m from the downwind edge of the spray swath, the drift deposition was 1.7% and 0.53% of the deposition at 0 mfor T1 and T2, respectively. T1 also produced an approximate two-fold increase over T2 in airborne material at 50 mdownwind of the spray swath edge at heights up to 10 m. These results were valid for spray applications made in crop canopiesor over concrete runways. The field results were compared to spray deposits predicted by the USDA Forest Service modelAgDISP. The model data in both datasets showed higher spray flux (i.e., more material moving through the air) for T1 thanfor T2, as was found in the field data. Depending on the height selected, AgDISP predicted an approximate two- to five-foldincrease in spray material moving 50 m downwind over a runway as compared to if a canopy was present. The results highlightthe need for aerial applicators to consider all of the droplet spectra data when selecting the most appropriate spray nozzlefor a given application situation. The data also suggest that ASAE Standard S572 may need to be modified in the future tobetter characterize nozzles that the cross nozzle classification lines defined in the standard.